1. Field of the Invention
The present invention relates to a storage device and a method of connecting a storage device to a host computer. More particularly, the present invention relates to a technique of connecting a storage device to a host computer when the system power supply is turned on, and when the hot plug (hot swap or concurrent firmware upgrade) is carried out.
2. Description of the Related Art
In order to set a storage device to a ready state, a certain constant time is necessary after a power supply is turn on. Specifically, in a Redundant Array of Independent (or Inexpensive) Disks device (RAID device), for example, several tens of seconds to a few minutes are necessary to spin up the hard disk drives (HDDs). Further, because it is also necessary to restore a saved RAID configuration, the storage device cannot be set to a ready state immediately after the power supply is turned on.
However, when a host interface is enabled, after the storage device becomes ready, by completely ending a POST process of the power supply to the storage device, there is a risk that a host computer cannot carry out a device scan in time and cannot recognize the storage device.
To overcome this difficulty, at the power-on time, the host interface is enabled in advance even when the storage device is not yet ready, thereby making the host computer recognize the storage device so that the storage device can be connected to the host computer.
There is a proposal of a data reading control system in a magnetic disk device as described in Japanese Unexamined Patent Publication No. 61-061264, for example. According to this proposal, in a magnetic disk device, in order to read data in a shortest waiting time after a motor is turned on (i.e., spin up), a data reading command is given to a magnetic disk control large-scale integration (LSI) by turning on the motor, and detection of an address mark in a read data signal from the magnetic disk is started. With this arrangement, a data reading operation is made possible before a ready signal actually becomes active.
Conventionally, a RAID device has a hot plug function (hot swap of a component or concurrent firmware upgrade within the system), without affecting the operation. This hot plug function is also provided in various kinds of storage devices, including a magnetic tape recording unit, and not only in the RAID device.
At the hot plug time, when the host interface is enabled in advance even when the storage device is not yet ready after the power supply is turned on, there is a risk of the occurrence of an inconvenience. When the storage device responds as not ready when the host computer accesses the storage device triggered by the enabling of the host interface (for example, when the Fibre Channel (FC) and the Internet Small Computer System Interface (iSCSI) are linked up), the host computer decides that this storage device has a problem. As a result, the host computer fails in making a reconnection in some cases.
The FC is one of interfaces able to carry out a serial transfer. The FC makes it possible to carry out a high-speed transfer and a long-distance transfer between the host computer and the storage device. The iSCSI is a protocol standard to carry out a transmission and reception of data via the Internet Protocol (IP) network, by covering the SCSI command/data in a transmission frame of a Transmission Control Protocol/Internet Protocol (TCP/IP) packet.
As explained above, in the connection of the storage device to the host computer (i.e., a boot processing of the controller), the connection processing suitable for execution after the power supply to the storage device is turned on has a risk of the occurrence of a problem when the storage device is connected to the host computer at the hot plug time.